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Cui J.B.,Innopower | Shu B.,Beijing Institute of Technology | Tian B.,Innopower | Sun Y.W.,Innopower | And 11 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2013

The function of the superconducting bias coil in a saturated iron-core fault current limiter is to magnetize the iron cores. For practical utility devices of HV power grids, the rated capacity is usually 100 MVA or higher. The size and weight of the iron cores of a saturated iron-core fault current limiter with such capacity is quite large, so the bias coil needs to have high magnetization capacity and consequently a large diameter. The stability and safety of the bias coil are of critical importance for the reliability required by power utilities. Experience taught us that great care must be taken in the design, fabrication, testing, and grid operation to avoid potentially fatal risks. In this paper, we will discuss and analyze the possible safety hazards for a large size superconducting bias coil, which may result in mechanical failure and electrical impact, causing significant damage to the coil. Possible causes of the hazards are improper configuration, mismatch of component materials during thermal cycling, manufacturing failures in fabrication, lack of protection in testing and operation, etc. We will also report measures we took to eliminate or reduce these safety hazards. © 2002-2011 IEEE.


Xin Y.,Innopower | Zhang J.,Innopower | Gong W.,Innopower
IEEE Transactions on Applied Superconductivity | Year: 2010

In some circumstances, a superconducting dc magnetizing coil with a magnetic core may be subject to a large induced voltage surge due to coupling with other coils or a sudden break/close of its circuit. For instance, the superconducting bias coil in a saturated iron-core type fault current limiter may experience a huge induced voltage when a short-circuit fault takes place in the power grid. These events may result in damage of the coil or other elements in the circuit. Therefore, it is important to have a measure for protecting the superconducting coil from large voltage surges. We designed a circuit configuration that is capable of suppressing voltage surges on the dc superconducting coil and has no adverse effect on the coil's normal magnetizing capacity. Experiments were carried out to verify the validity of the design. In this paper, we introduce the protective circuitry and its work principle. We also report the experimental results which are in a good agreement with theoretical calculations. © 2006 IEEE.

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